DE102004061389A1 - Biaxially oriented polyester film containing silica and titania - Google Patents

Abstract

The invention relates to a biaxially oriented polyester film, which is composed of at least one base layer (B), the 0.25 to less than 1.0 wt .-% SiO¶2¶ and 0.25 to less than 1.0 wt .-% TiO Contains ¶2¶. The invention further relates to a process for the production of the film and its use. The film according to the invention is characterized by characteristic surfaces and defined optical properties and is well suited for use in the industrial sector.

Description

The invention relates to a biaxially oriented polyester film which is composed of at least one base layer (B) containing 0.25 to <1.0 wt .-% SiO ₂ and 0.25 to <1.0 wt .-% TiO ₂ , The invention further relates to a process for the production of the film and its use.

The inventive film is characterized by characteristic surfaces and defined optical properties out and is for the use in the industrial sector well suited.

The Industry has a high demand for plastic films such. B. biaxial oriented polypropylene or biaxially oriented polyester films, the defined surfaces and optical properties. Slides with uniform, not too high surface roughness are of interest in special applications.

In US-A-3,154,461 discloses a process for producing a biaxial oriented film of thermoplastic material (eg polyethylene terephthalate, Polypropylene) with a matt surface in which the film comprises incompressible particles (eg calcium carbonate, Silicon dioxide) in a size of 0.3 up to 20 μm and in a concentration of 1 to 25% by weight. Furthermore, in this Registration of the matt film produced by the process according to the invention, claimed. For Many applications are those produced by the process of the invention Film too rough.

EP-A-1 197 326 describes a matt, biaxially oriented polyester film which contains 1 to 10% by weight of particles having an average particle size of 2 to 5 μm. The mean roughness R _{a of} these films is in the range of 150 to 1000 microns. About the uniformity of the roughness and the height of the highest surveys, no statements are made.

In EP-B-0 152 265 describes a polyester film which is 0.01 to 1.0% by weight of silica and / or titanium dioxide having a mean Particle size of 0.01 up to 0.5 μm and 0.02 to 0.5 weight percent calcium carbonate having a mean particle size of 0.04 to 0.48 μm contains. This film has a very low due to the small particles Roughness, about the transparency is not made statements.

The JP-A-62-241928 describes a film comprising titanium dioxide, silica and an optical brightener. The concentration of titanium dioxide is in the range of 8 to 20 wt .-%, thereby the film has a very low transparency.

In EP-A-0 723 565 claims a polyester film comprising 1 to 20 wt .-% titanium dioxide and 0.1 to 6 wt .-% mica with a medium Particle size of 3 up to 40 μm contains. Due to the high amount of titanium dioxide, the transparency is too low.

In US-A-5,403,879 claims a polyester film, the 5 bis 25 wt .-% titanium dioxide, 0.1 to 3 wt .-% silica with a middle Particle size of 1 up to 5 μm and 0.02 to 1.0% by weight of a fluorescent organic pigment contains. Due to the high concentration of titanium dioxide, the film has a very low transparency. In the examples, films with a Transparency of less than 2% called at a film thickness of 188 microns.

The object of the present invention was to provide a biaxially oriented polyester film which has a uniformly low roughness and defined optical properties. In particular, the transparency of the film should be in the range of 30 to 90%. The structure of the surface should cause the film to be well processed and coated. There must be no high peaks (R _p over 4 μm). These would lead to defects in the coating. Such films are z. In applications where the surface topography of the film is transferred to a substrate, and especially when the film is coated with a release layer which adheres to the substrate.

The object is achieved by a biaxially oriented polyester film with at least one matte base layer (B), which contains both silicon dioxide for generating the surface roughness and titanium dioxide for adjusting the transparency. The concentration of the two fillers is in each case 0.25 to <1.0 wt .-%, preferably 0.3 to 0.95 wt .-%, particularly preferably 0.35 to 0.9 wt .-%, based on the total weight of the film. By correspondingly varying the concentration of the two fillers, roughness and transparency values which are within the desired range are achieved for films of different thicknesses.

• • Die höchste Erhebung auf der Folie (R_P) ist kleiner 4,0 μm, bevorzugt kleiner 3,5 μm und besonders bevorzugt kleiner 3,0 μm.
• • Die Größe der SiO₂-Partikel liegt zwischen 0,5 μm und 3,0 μm, bevorzugt zwischen 1,0 μm und 2,8 μm und besonders bevorzugt zwischen 1,5 μm und 2,5 μm (d₅₀). Das Siliziumdioxid ist bevorzugt amorphe Kieselsäure. Die Ausdehnung der SiO₂-Partikel sollte in alle Raumrichtungen ungefähr gleich groß sein, d. h. das Verhältnis von Länge zu Breite zu Höhe sollte nahe bei 1:1:1 liegen, bevorzugt bei (0,9–1,1):(0,9–1,1):1.
• • Die Transparenz der Folie liegt im Bereich zwischen 30 und 90 %, bevorzugt zwischen 40 und 80 % und besonders bevorzugt zwischen 50 und 70 %.
• • Das Titandioxid kann sowohl vom Rutil-Typ als auch vom Anatas-Typ sein. Die Korngröße des Titandioxids liegt bevorzugt zwischen 0,02 und 0,6 μm, bevorzugt zwischen 0,05 und 0,5 μm und besonders bevorzugt zwischen 0,1 und 0,4 μm.
• • Die Zahl der Erhebungen auf der Oberfläche der Folie, die höher als 0,1 μm sind, liegt zwischen 800 und 10000 pro mm², bevorzugt zwischen 1000 und 7500 pro mm² und besonders bevorzugt zwischen 1200 pro mm² und 5000 pro mm².
• • Der Glanz der Folie, gemessen bei 60°, liegt zwischen 20 und 100, bevorzugt zwischen 30 und 85 und besonders bevorzugt zwischen 40 und 70.

The film according to the invention preferably has the following properties:

• The highest elevation on the film (R _P ) is less than 4.0 μm, preferably less than 3.5 μm and particularly preferably less than 3.0 μm.
• The size of the SiO ₂ particles is between 0.5 μm and 3.0 μm, preferably between 1.0 μm and 2.8 μm and particularly preferably between 1.5 μm and 2.5 μm (d ₅₀ ). The silica is preferably amorphous silica. The extent of the SiO ₂ particles should be approximately the same in all spatial directions, ie the ratio of length to width to height should be close to 1: 1: 1, preferably at (0.9-1.1) :( 0, 9 to 1.1):. 1
• The transparency of the film is in the range between 30 and 90%, preferably between 40 and 80% and particularly preferably between 50 and 70%.
• The titanium dioxide can be both rutile and anatase type. The particle size of the titanium dioxide is preferably between 0.02 and 0.6 μm, preferably between 0.05 and 0.5 μm and particularly preferably between 0.1 and 0.4 μm.
• The number of elevations on the surface of the film which are greater than 0.1 μm is between 800 and 10,000 per mm ² , preferably between 1,000 and 7,500 per mm ^2, and particularly preferably between 1,200 per mm ² and 5,000 per mm ² ,
• The gloss of the film, measured at 60 °, is between 20 and 100, preferably between 30 and 85 and particularly preferably between 40 and 70.

According to the invention Foil preferably monolayer and includes in this Case as a layer only the base layer (B).

The Base layer (B) of the film contains preferably at least 70% by weight of thermoplastic polyester. Suitable for that are polyesters of ethylene glycol and terephthalic acid (= polyethylene terephthalate, PET), ethylene glycol and naphthalene-2,6-dicarboxylic acid (= polyethylene-2,6-naphthalate, PEN), from 1,4-bis-hydroxymethyl-cyclohexane and terephthalic acid [= poly (1,4-cyclohexanedimethylene terephthalate), PCDT] and ethylene glycol, naphthalene-2,6-dicarboxylic acid and Biphenyl-4,4'-dicarboxylic acid (= polyethylene-2,6-naphthalate bibenzoate, PENBB). Particularly preferred are polyesters which are at least 90 Mol%, preferably at least 95 mol%, of ethylene glycol and terephthalic acid units or consist of ethylene glycol and naphthalene-2,6-dicarboxylic acid units. In a very preferred embodiment For example, the base layer is polyethylene terephthalate homopolymer.

Suitable other aliphatic diols are, for example, diethylene glycol, triethylene glycol, aliphatic glycols of the general formula HO- (CH ₂ ) _n -OH, where n is an integer from 3 to 6, (in particular propane-1,3-diol, butane-1, 4-diol, pentane-1,5-diol and hexane-1,6-diol) or branched aliphatic glycols having up to 6 carbon atoms. Of the cycloaliphatic diols, mention may be made of cyclohexanediols (in particular cyclohexane-1,4-diol). Suitable other aromatic diols correspond, for example, to the formula HO-C ₆ H ₄ -XC ₆ H ₄ -OH, where X is -CH ₂ , -C (CH ₃ ) ₂ , -C (CF ₃ ) ₂ , -O-, - S- or -SO ₂ is. In addition, bisphenols of the formula HO-C ₆ H ₄ -C ₆ H ₄ -OH are also very suitable.

Other aromatic dicarboxylic acids are preferably benzenedicarboxylic acids, naphthalenedicarboxylic acids, for example naphthalene-1,4- or 1,6-dicarboxylic acid, biphenyl-x, x'-dicarboxylic acids, in particular biphenyl-4,4'-dicarboxylic acid, diphenylacetylene-x, x'- dicarboxylic acids, in particular diphenylacetylene-4,4'-dicarboxylic acid, or stilbene-x, x'-dicarboxylic acids. Of the cycloaliphatic dicarboxylic acids, mention may be made of cyclohexanedicarboxylic acids, in particular cyclohexane-1,4-dicarboxylic acid. Of the aliphatic dicarboxylic acids, the (C ₃ to C ₁₉ ) alkanedioic acids are particularly suitable, it being possible for the alkane part to be straight-chain or branched.

The if applicable, additional (s) Layers (intermediate or outer layers) of the film are preferred also made of a polyester, as described above for the base layer was, wherein the composition is the same or different from that of the base layer.

The Preparation of the polyester can z. B. after the transesterification process respectively. It is based on dicarboxylic acid esters and diols, the with the usual Transesterification catalysts such as zinc, calcium, lithium, magnesium and manganese salts be implemented. The intermediates are then in the presence generally more common Polycondensation catalysts such as antimony trioxide or titanium salts polycondensed. The production can be just as good after the direct esterification process in the presence of polycondensation catalysts. there starting directly from the dicarboxylic acids and diols.

The film according to the invention contains both SiO ₂ particles and TiO ₂ particles to produce the desired surface properties and appearance.

The SiO ₂ particles are in the film in an amount of 0.25 to <1.0 wt .-%, preferably 0.3 to 0.95 wt .-%, particularly preferably 0.35 to 0.9 wt. -%, (based on the total weight of the film). If the film is multi-layered, then the indicated amount of SiO ₂ particles is contained at least in an outer layer. If less than 0.25 wt .-% present, so are too few projections on the surface of the film. If 1.0 or more than 1.0 wt% is present, the surface becomes inhomogeneous because particles on the surface are pushed up by particles underneath. The SiO ₂ particles preferably have an average particle size of from 0.5 to 3.0 μm, preferably from 1 to 2.8 μm and particularly preferably from 1.5 to 2.5 μm (d ₅₀ ). If the particles are larger than 3.0 μm, the elevations are too high and lead to coating errors. The extent of the SiO ₂ particles should be approximately the same in all spatial directions, ie the ratio of length to width to height should be close to 1: 1: 1, preferably at (0.9-1.1) :( 0, 9 to 1.1):. 1 As silicon dioxide particles, amorphous silica particles are preferably used.

The TiO ₂ particles are likewise present in the film in an amount of 0.25 to <1.0% by weight, preferably 0.3 to 0.95% by weight, particularly preferably 0.35 to 0.9% by weight .-%, (based on the total weight of the film, even if the film is multi-layered). If less than 0.25% by weight is present, the transparency is too high. If 1.0 or more than 1.0 wt% is present, the transparency is too low. The TiO ₂ particles preferably have an average particle size (d ₅₀ ) of 0.02 to 0.6 μm, preferably of 0.05 to 0.5 μm and particularly preferably of 0.1 to 0.4 μm. If the particles are smaller than 0.02 μm, agglomerates readily form. If the particles are larger than 0.6 μm, they affect the roughness. The titania particles can be both rutile and anatase types.

The combination of the SiO ₂ particles and TiO ₂ particles has the effect that the highest elevation on the film (R _p ) is less than or equal to 4.0 μm, preferably less than or equal to 3.5 μm and particularly preferably less than or equal to 3.0 μm. If it is greater than 4.0 microns, so pierce these tips applied in a further processing step coating. The total number of elevations on the surface of the film that are greater than 0.1 μm is between 800 and 10,000 per mm ² , preferably between 1,000 and 7,500 per mm ^2, and particularly preferably between 1,200 per mm ² and 5,000 per mm ² . If it is smaller than 800 per mm ² , it causes problems in processing.

The combination of the SiO ₂ particles and TiO ₂ particles additionally causes the transparency of the film to be between 30 and 90%, preferably between 40 and 80% and particularly preferably between 50 and 70%.

The base layer (B), in addition to the SiO ₂ and TiO ₂ particles still contain conventional additives such as stabilizers. As stabilizers are advantageously used, for example, phosphorus compounds such as phosphoric acid or phosphoric acid esters. Other particles which influence the surface properties and / or appearance of the film, such as CaCO ₃ particles are preferably not present in the film according to the invention.

The Thickness of the polyester film according to the invention can vary within certain limits. It is advantageous in the range of 10 to 350 μm, in particular from 15 to 300 μm, preferably from 20 to 250 microns.

Production method:

The The invention also relates to a process for the preparation of the polyester film according to the invention according to the known per se from the literature extrusion process (see for example: "Handbook of Thermoplastic Polyesters, Ed. S. Fakirov, Wiley-VCH, 2002 "or in the chapter" Polyesters, Films "in the" Encyclopedia of Polymer Science and Engineering, Vol. 12, John Wiley & Sons, 1988 ").

in the Under this procedure, the procedure is that of the film corresponding melt is extruded through a flat die, the so obtained film for solidification on one or more roller / s deducted will, then the slide biaxially stretched (oriented), the biaxially stretched film heat-set and optionally on the surface layer intended for the treatment is still corona or flame treated.

The biaxial stretching (orientation) is generally performed consecutively, with the successive biaxial stretching, first longitudinal (in the machine direction) and then transverse (vertical) right to the machine direction), is preferred.

First, as usual in the extrusion process, the polymer or the polymer mixture for the film in an extruder compressed and liquefied, where appropriate as additives provided additives already in the polymer or in the polymer mixture may be included. The melt is then simultaneously pressed through a flat die (slot die), and the squeezed melt is deposited on one or more cooled draw rolls withdrawn, the melt cools and becomes a prefilm solidified.

The Biaxial stretching is generally performed sequentially. there Preferably, the prefilm is first longitudinally (i.e., in the machine direction = MD direction) and subsequently in the transverse direction (i.e., perpendicular to the machine direction = TD direction) stretched. this leads to to a spatial Orientation (orientation) of the polymer chains. The stretching in the longitudinal direction let yourself with the help of two different according to the desired stretch ratio fast rotating rollers. Used for cross stretching you generally have a corresponding clip frame in which the film on both edges clamped and then at elevated Temperature is drawn to both sides.

The Temperature at which the stretching is carried out can be done in a relative huge Range vary and depends on the desired properties of the film. In general, the longitudinal stretching is at a temperature in the range of 80 to 130 ° C and the transverse extent in the range from 80 to 150 ° C carried out. The longitudinal stretching ratio is generally in the range of 2.5: 1 to 5: 1, preferably from 3: 1 to 4.5: 1. The Transverse stretching ratio is generally in the range of 3.0: 1 to 5.0: 1, preferably 3.5: 1 to 4.5: 1.

at the subsequent heat setting is the film over a Duration of about 0.1 to 10 seconds at a temperature in the range from 150 to 250 ° C held. Subsequently The film is in the usual Wrapped up way.

To the biaxial stretching can one or both surfaces the film corona- or flame-treated according to one of the known methods become. The treatment intensity is adjusted so that a surface tension in the range of about 45 mN / m established.

to Setting further desired Properties can add the foil in addition be coated. Typical coatings are adhesion-promoting, antistatic, slip-improving, hydrophilic or dehesivative. It lends itself to these extra Layers over In-line coating by means of aqueous Dispersions after the stretching step in the longitudinal direction and before the stretching step in the transverse direction to apply to the film.

at the production of the film according to the invention is ensured that the waste material (regenerate) in an amount in the range of up to 70 wt .-%, based on the total weight of the film, again the Extrusion supplied can be, without doing the physical properties of the Slide are negatively influenced, especially not her visual appearance.

The inventive film is characterized by defined optical properties and a uniform roughness out. The following Table 1 gives the properties of the films of the invention contrary.

Table 1

by virtue of their properties, the films of the invention are suitable for the production of less shiny, rough surfaces on different substrates, especially when first applying thin layers to the film be applied. In this case it comes through the low, uniform roughness for homogeneous coating of the surface. A formation of holes or thin places in the coating is prevented. Particularly preferred is the Application as transfer and release film.

to Characterization of the raw materials and the films were in the frame the present invention uses the following measurement methods:

SV value (standard viscosity)

The standard viscosity SV (DCE) is measured, based on DIN 53726, in dichloroacetic acid.

The intrinsic viscosity (IV) is calculated from the standard viscosity as follows IV (DCE) = 6.907 x 10 -4 SV (DCE) + 0.063096

shine

Of the Gloss was determined according to DIN 67 530. The reflector value was measured as an optical parameter for the surface of a Foil. Based on standards ASTM-D 523-78 and ISO 2813 the angle of incidence is set at 60 °. A light beam hits below the set angle of incidence the flat test surface and is reflected or scattered by this. The on the photoelectronic receiver striking light rays are called proportional electric Size displayed. The measured value is dimensionless and must match the angle of incidence be specified.

Measurement of the mean diameter d ₅₀

The determination of the mean diameter d ₅₀ was carried out by laser on a Malvern Master Sizer according to the standard method (other measuring devices are for example Horiba LA 500 or Sympathec Helos, which use the same measuring principle). The samples were placed in a cuvette with water and then placed in the meter. The measuring process is automatic and includes the mathematical determination of the d ₅₀ value.

By definition, the d ₅₀ value is determined from the (relative) cumulative curve of the particle size distribution: the point of intersection of the 50% ordinate value with the cumulative curve immediately gives the desired d ₅₀ value on the abscissa axis. How to understand this will be in 1 clarified in more detail.

Highest collection, number of surveys

The highest elevation on the film and the number of elevations were determined using a white light interferometry microscope made by Veeco, type Wyko NT3300. For measurement, a piece of film 10 × 10 cm in size was placed on the table of the microscope and weighted for fixing with a metal ring with a diameter of 5 cm. An area of 0.9 mm x 1.2 mm at 5.1x magnification was measured, the individual measuring points are 1.65 μm apart. A possible waviness of the pattern was filtered out. The maximum elevation R _P is the distance from the calculated center plane (mean of all measuring points) to the highest point in accordance with DIN EN ISO 4287.

For the determination the number of the survey was defined as follows. A survey or peak is a measuring point that is at least 0.1 μm higher (in the z direction) as his four next Neighbors (in x and y direction) and which is higher than 20% of the height of the highest elevation. The mean values from 5 individual measurements are given in each case.

transparency

The The polyester films are measured on the Hazegard Hazemeter XL-211 BYK Gardner according to ASTM-D 1003-00.

in the The invention will be explained in more detail below with reference to examples.

example 1

crisps of polyethylene terephthalate were dried and the extruder for the base layer (B) supplied. Then by extrusion and subsequent stepwise orientation in longitudinal and transverse direction of a single-layer film with a total thickness of 100 μm produced.

Foil, mixture of:
75 wt .-% polyethylene terephthalate with an SV value of 800
25 wt .-% masterbatch of 96 wt .-% polyethylene terephthalate, 2.0 wt .-% silica particles having a d ₅₀ value of 2.0 microns and 2.0 wt .-% titanium dioxide with a d ₅₀ value of 0 , 2 μm.

The production conditions in the individual process steps were:

The Film had the required uniform low roughness and the required transparency. The achieved properties of the film are shown in Table 2.

Example 2

Compared to example 1, the composition of the film was changed as follows: film, mixture of:
60 wt .-% polyethylene terephthalate with an SV value of 800
40 wt .-% masterbatch of 96 wt .-% polyethylene terephthalate, 2.0 wt .-% silica particles having a d ₅₀ value of 2.0 microns and 2.0 wt .-% titanium dioxide with a d ₅₀ value of 0 , 2 μm.

The Roughness of the film has increased compared to Example 1, the Transparency reduced.

Example 3

Compared to example 1, the composition of the film was changed as follows: film, mixture of:
75 wt .-% polyethylene terephthalate with an SV value of 800
25 wt .-% masterbatch of 96 wt .-% polyethylene terephthalate, 2.0 wt .-% silica particles having a d ₅₀ value of 2.5 microns and 2.0 wt .-% titanium dioxide with a d ₅₀ value of 0 , 2 μm.

The Roughness of the film has increased compared to Example 1.

Comparative Example 1

Compared to Example 1, the film was now produced with a particle system according to EP-A-1 197 326. The examples of EP-A-1 197 326 have SiO ₂ contents which are from 2 to 3% by weight. A comparison was made with a particle concentration closer to the subject of the present invention (1.0% by weight). The roughness of the film is too high.

Foil, mixture of:
80 wt .-% polyethylene terephthalate with an SV value of 800
20 wt .-% masterbatch of 95 wt .-% polyethylene terephthalate and 5.0 wt .-% silica particles with a d ₅₀ value of 3.4 microns.

Claims (16)

Biaxially oriented polyester film, which is composed of at least one base layer (B) containing 0.25 to less than 1.0 wt .-% SiO ₂ and 0.25 to less than 1.0 wt .-% TiO ₂ . Polyester film according to claim 1, characterized in that the highest elevation on the film (R _P ) is less than 4.0 microns. Polyester film according to claim 1 or 2, characterized in that the size of the SiO ₂ particles is between 0.5 μm and 3.0 μm (d ₅₀ ). Polyester film according to one of claims 1 to 3, characterized in that the SiO _{2 is} preferably amorphous silica. Polyester film according to one of claims 1 to 4, characterized in that the expansion of the SiO ₂ particles is approximately equal in all directions in space. Polyester film according to one of claims 1 to 5, characterized in that the TiO _{2 is of} the rutile type or of the anatase type. Polyester film according to one of claims 1 to 6, characterized in that the size of the TiO ₂ particles is between 0.02 and 0.6 microns (d ₅₀ ). Polyester film according to one of claims 1 to 7, characterized in that the transparency of the film in the range between 30 and 90%. Polyester film according to one of claims 1 to 8, characterized in that the number of elevations on the surface of the film, which are higher than 0.1 microns, between 800 and 10,000 per mm ² . Polyester film according to one of claims 1 to 9, characterized in that the gloss of the film, measured at 60 °, between 20 and 100 lies. Film according to one of claims 1 to 10, characterized that she is single-layered. Film according to one of claims 1 to 11, characterized that - apart of optionally present catalyst precipitates - contains no further particles. Film according to one of claims 1 to 12, characterized that it has a thickness of 10 to 350 microns. A process for producing a film according to claim 1, wherein a polyester polymer is melted in at least one extruder and the obtained polymer melt according to the composition of the film layer of a nozzle or the polymer melts obtained corresponding to the compositions of the cover and base layers of a multi-layer nozzle, from the nozzle to a Cooling roller extruded and then the biaxially stretched and heat-fixed, the polymer melt for the base layer 0.25 to less than 1.0 wt .-% SiO ₂ and 0.25 to less than 1.0 wt .-% TiO ₂ . Use of a film according to claim 1 in industrial Sector. Use according to claim 11 as a release or transfer film.